Rather than keeping track of each demand observation, Betty Sucasas, a member of the marketing staff with a large company that produces a line of switches, has kept only grouped data. For switch C9660Q, used in small power supplies, she has observed the following numbers of units of the switch shipped over the last year.

Number of Units Shipped Weeks 0–2,000 3 2,001–5,000 6 5,001–9,000 12 9,001–12,000 17 12,001–18,000 10 18,001–20,000 4 Based on these observations, estimate the mean and the standard deviation of the weekly shipments. (Hint: This is known as grouped data. For the purposes of your calculation, assume that all observations occur at the midpoint of each interval.)